Process for making metallic cerium and the like.



A. & M. HIRSCH.

PROCESS FOR MAKING METALLIC CERIUM AND THE LIKE.

APPLICATION FILED SEPT. 1. 1917.

1 273,223 Patented July 23, 1918 2 my I'VTORS @mg/ A TTORNEY r an op nion.

ALCAN HIRSCH AND MARX HIRSCH, OF NEW YORK, N. Y., ASSIGNORS TO ALPHA MANUFACTURING COMPANY, A CORPORATION OE NEW YORK.

PROCESS FOR MAKING METALLIC CERIUM AN D THE LIKE.

Specification of Letters Patent.

Patented July 23, 1918.

Application filed September 1, 1917. Serial No. 189,271.

To all whom it may concern:

Be it known that we, ALCAN Hmsorr and MARX HIRsoH, citizens of the United States, and residents of New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Processes for Making Metallic Cerium and the like, of which the following is a specification.

Our invention relates to improvements in processes for making metallic cerium and the like, and more particularly to the production of metallic cerium and similar rare earth metals, such as misch-metall, comprising mainly metallic cerium alloyed with small'quantities of other rare earth metals, such as lanthanum, didymium, erbium and thorium, by electrolysis.

While experimental literature describes certain methods of obtaining these metals on a laboratory scale, we have found that, when it was attempted to produce such metal on a large scale by following such literature, man-y difliculties were encountered which rendered the manufacture wholly uncommercial.

Accordingly, the main object of the present invention is to provide improvements whereby the metal may not only be obtained continuously on a large scale, but easily and efficiently, from cheap raw material and in relatively pure form at low cost.

Further and more specific objects, features and advantages will more clearly appear from the description given below, taken in connection with the accompanying sheet of drawings, which form a part of this specification.

In the drawings,

Figure 1 is a vertical section illustrating one form of apparatus by means of which the electrolysis may be carried out; and

Fig. 2 is a vertical section illustrating a preferred method of locating the cathode if clay pots are used.

We have discovered that, to secure an electrolyte suitable for the prolonged regular commercial production of metallic cerium, certain peculiar precautions are necessary. We believe these to be connected with the surface'tension between electrolyte and metal, and, therefore, call them tension conditions, though their importance may be due partly or wholly to other causes. We have alsofound that certain rather limited ranges of temperature are required for efiiciently performing the two classes of work to be carried out in the electrolytic cell, and these we denominate separating temperature and agglomerating temperature, as hereinafter described. Furthermore, we have found that the distribution of heat in the cell and method of conveying supplementary heat to the cell are of importance in securing practical results and commercially economical yields. We have further discovered that electrolyte apparently useless and exhausted can, by the exercise of suitable precautions, be made to yield up part or all of its metallic content, and that, in removing metalfrom the cells when produced and separated, certain precautions are desirable, if not essential.

In the preparation of the electrolyte, instead of using the natural cerium minerals we prefer to utilize the mixed waste obtained in the manufactures of thorium or lanthanum, and occurring as a yellowish mud, largely oxids of cerium and others of the metals mentioned, in one of the processes in the gas mantle industry, and occurring as an impure solution of chlorids of the metals in another such process.

The former we prefer to dissolve up in commercial hydrochloric acid, reasonably free of sulfuric acid and sulfates, using during the solution process as little heat as possible, and preferably maintaining an excess of the yellowish mud. so as to make the chlorids of the metal. The resulting chlorid liquor in either case consists,'not of cerium chlorid, but of a mixture of the chlorids of cerium, lanthanum, didymium, erbium, tho- Y rium and other rare earth metals of which cerium is the chief single constituent. Contrary to common belief, the general purity of this solution is immaterial, but the percentages of sulfur and phosphorus compounds on the one hand, or ofchlorin carriers of dual valency, such as iron and aluminum compounds, on the other hand, should each be reduced below 3%. Addition of an excess of cerium oxid may be used to throw out the iron and aluminum and calcium chlorid, or, better, barium chlorid may be used to throw out the sulfur and phosphorus. The solution is then clarified, preferably hot, by filtration or settling, and evaporated to dryness.

The preparation of electrolyte should be so carried out as to secure the 'roper tension conditions between the fused e ectrolyte and the fused metal when produced in the electrolytic bath. An excess of certain impurities, including oxychlorinated products, such as cerium oxychlorid, we believe tends to so far reduce the surface tension between metal and electrolyte in the electrolytic bath, and alter the viscosity, as to produce emulsification or colloidal solution of metal in the fused electrolyte and prevent amalgamatiOn 0f the metal in the bath.

The oxychlorids may be removed in either of two ways.

First wag .The chlorid solution obtained as above may be evaporated to solidification and then fused in an atmosphere ofhydrochloric acid gas to produce complete dehydration while preventing oxidation by the air or decomposed steam from the electrolyte, the aqueous acid in the vapors being, if desired, condensed hot and separated, and the concentrated hydrochloric acid gas may be dried and used over again, or may be recovered with water as hydrochloric acid and set aside for further use in dissolving oXid, the yellow mud mentioned, or cerium carbonate, to produce further electrolyte. In" this manner sufiiciently pure chlorids can be prepared to be added to the electrolytic bath and long-continued operation of a single cell is permitted.

Second way.-The known method of making for electrolysis the double chlorid of sodium and cerium does not yield a desir-;. able electrolyte, and if, instead of sodium chlorid, ammonium chlorid be used, with cerium chlorid, to make the electrolyte,

satisfactory results on a commercial scale are not obtained, but we have found that, if about 15% sodium or potassium chlorid (insufficientto make the double salt) and 15 7a of ammonium chlorid by weight, based on the dry weight of the dissolved rare earth chlorids, are both added to the chlorids, after the excess of iron, aluminum, sulfur and phosphorus impurities are removed and before the evaporation, the solution may then be evaporated to dryness and the crystallizing point and the dehydration carried through to fusion of the chlorid without the roduction of characteristics resulting in obectionable tension phenomena in the electrolytic bath when the material is later subjected to electrolysis. Although 15% of sodium chlorid is thus added to the material,

the dehydrated electrolyte after fusion is generally found to contain less than 9% sodium chlorid. The ammonium chlorid is Volatilized in the above treatment and forms a chlorinating agent as does the HCl gas in the first way, and may be similarly recovered and reintroduced into the process.

When the electrolyte formed in this way is subjected to electrolysis, the alkali metal chlorid accumulates in the electrolytic cell, and after the removal of the metallic cerium or misch-metall, it may be thrown away or dissolved in hydrochloric acid, clarified, purified as above explained, and added to fresh electrolyte being prepared.

Either of these operations is best carried out in deep cast-iron vessels suitably heated in a manner to produce even and equable temperature, for which purpose thick castings, high in carbon and silicon, are preferred to wrought iron, and large quantities of electrolyte, in excess of 100 pounds, are more satisfactorily handled than numerous small batches. When fusion of the batch begins, it is best continued and the batch boiled for a period of about twenty minutes, or until boiling practically ceases to eliminate all objectionable volatile C0111- pounds.

The fused electrolyte thus prepared may be added to the electrolytic cell as such, but is preferably first cast in shallow iron pans or on iron plates, then broken up and stored in a dry place to be used, as hereinafter described, in controlling the temperature of the electrolytic cell, as well as for merely furnishing the raw material for electrolysis.

The electrolysis is preferably carried'out in pots of similar cast-iron, high in carbon and silicon, although it may be carried out in suitable clay crucibles about a footin diameter and 12 to 18 inches deep, usually set in brick work, and externally heated. The heat should not be applied, as would ordinarily be the case, to the sides of the pot. We apply it almost wholly to the bottom of the pot and carefully regulate its intensity and volume. The preferable means of heating is by a gas flame blast torch, though liquid fuel or any suitable equivalent easily regulated and capable of local application may be used. We have found it very objectionable to fill the pot with fused electrolyte, as described in experimental literature, and then make additions as it is consumed. We begin electrolysis with a nearly empty pot, heat a small amount of electrolyte, preferably that obtained by the tsecond way, with the outside gas flame, nearly to fusion and apply the electric current to complete the fusion, thereafter continuing the electrolysis and the gradual ad- .dition of electrolyte, building up the charge For the size of pot above indicated, it is best to start withv only about 5 pounds of electrolyte made in the second way. V'Ve have found that either carbon or graphite anodes may be used, but we have discovered they each show a critical current density, 2' 6., one above which current may pass without valuable effect. For graphite this is about 6 to 7 amperes per square inch of anode surface, and for carbon about 5:} amperes per square inch of anode surface. Furthermore, we find it desirable to maintain a relation between current density at the anode and at the cathode, the latter being about one-fourth to one-third of the former in order to secure a desirable electrical circulating and heating effect.

In this example of the electrolysis, a five or six-inch graphite electrode is preferred, and at first a current of only about 200 am peres permitted to flow. The voltage between electrodes is mentioned in experimental liter ature as 12 to 20 volts. We have found this to be injurious to the commercial operation of our process; in fact, practical commercial results cannot be obtained if 12 to 20 volts are maintained, because of local overheating and the formation of carbids, which thicken the bath and destroy what we believe to be proper tension conditions. The

voltage we use starts at about 12 volts and rapidly falls to about -7 volts or less as soon as regular operation is well under way.

During the first hour of operation about 1 pound of electrolyte, made either according to the first way or the second way, is added every ten or fifteen minutes, and the current is gradually increased from 200 to 900 amperes, during which the torch is used to regulate the temperature of the electrolyte to about 850 (1., so as to secure by the end of the first hour a clear bright yellow red, very actively electrolyzing bath. The

pound of electrolyte added every ten or fifteen minutes is in excess of the decrease in volume due to the electrolysis, so that the volume of the bath is increased beyond the original volume. When properly operating, this bath should show an active surface current of electrolyte traveling from the anode to the cathode pot and an active evolution of chlorin bubbles.

As the electrolysis proceeds, a skin forms around the edges of the pot, the activity of the electrolyte stream diminishes and the Y skin gradually approaches the anode. \Ve

have discovered that this is not congelation of the surface, as supposed, and increased temperature is not helpful at this time. This scum formation is believed to be due to the accumulation of exhausted impure electrolyte, the action of which, as a protective scum over the bath, we believe is de' sirable, butan excess of which, if permitted to accumulate, is highly objectionable. Be-

fore it reaches within an inch of the anode, therefore, regular building up of the charge should be resumed by adding electrolyte at the rate of about 2 pounds every half hour and the current gradually increased till the end of the second hour it reaches about 1200 to 1250 amperes, where it is held thereafter.

We have found that, about every two hours, the contents of the cell should be thoroughly stirred with the anode or with a fairly heavy one-inch iron rod to over come the tendency to form metallic growths in the electrolyte and to aid in agglomeration of the metal formed.

The bright yellow-red heat, about 850 C., is maintained substantially throughout the period of electrolysis. If electrolyte made according to the second way is alone used after starting the electrolysis, then, at the end of the run, or at suitable intervals during the run, the temperature is raised about 100 (l, to about 950 C., and the cell charge thoroughly agitated or stirred to facilitate agglomeration.

It has been customary to regulate ter1ninal voltages in electrolytic work by separately exciting the generator forming the source of current. This we avoid almost wholly, and at the same time gain another great advantage in regulating the terminal voltage, by carrying the anode on a support adapted to regulate accurately (say within one-eighth of an inch) the depth of its immersion in the fused electrolyte, and thereby maintain the electrode very elose to 2'. 6. less than one inch from the conducting body of metallized material at the bottom of the cell.' Thus, we are enabled, by slight adjustment of the electrode, to vary the terminal voltage without continual danger from short circuits in the cell, but, more important than this, We are enabled thereby to localize the heating effect of the two contact surfaces where the heat is needed and largely to localize the deposition of metal where it is most readily agglomerated and united with the mass of metal bein produced, instead of having it distributed throughout the bath. Thus, the anode is kept nearer to the metalliferous bottom of the charge as cathode than to any conductingpoint on the side of the pot, and conduction of current, together with deposition of metal, are brought together largely at the bottom.

We have discovered that, contrary to common belief, the electrolytic metal produced is not readily attacked. by the chlorin atmosphere in the cell, we believe because the surface of the molten metal is covered by a surface tension film of fused electrolyte, which seems to, be more impervious to chlorin gas than to the oxygen of the air. e, therefore, depart from previous practice, by closing in the top of the cell as much as is compatible with needed access for operation, preferably with a gas recovery hood, by means of which we are enabled to prevent the free access of the air to the cell, keep the electrolyte more uniformly heated at ,the surface, and restrain and collect the chlorin evolved in the electrolysis. We find that, in spite of the atmosphere of chlorin thus created, one serious difiiculty remains to be overcome, Z., e., the active corrosion of the anode just above the surface of the electrolyte where it is subjected to action of both heat and any oxygen present in the cell atmosphere. This was sought to be overcome by various protection hoods, etc., without success, until we discovered that satisfactory protection can be secured by bathing the electrode with molten electrolyte during the operation, to a distance of 4 to 6 inches above the line ofc'ontact with the electrolyte surface.

By adding solid lumps of electrolyte to the bath, we are able to regulate the temperature of the cell when it becomes slightly too hot, as well as to contribute a portion, at least, of the fresh electrolyte required for building up the charge being decomposed. These lumps inevitably accumulate some moisture on the surface, which moisture tends to cause oxidation of the charge. Also, their addition, perfectly cold, tends to cause irregularly thickened-or clotted portions of the electrolyte, so that we have found it most satisfactory to place these lumps, for a time before addition, on the'edge of the cell and allow them to become thoroughly dried in the chlorinated atmosphere of the hood, and also to become heated somewhere near to the fusion point before dropping them into the liquid electrolyte.

As the run app-roaches 24 to 26 hours in duration, if electrolyte made according to the second way is used, the sodium salt accumulates in the charge to such an extent that it becomes advisable to terminate the run. We have found that certain preparation for this termination is necessary to securing good yields of metal. In the first place, we have found that the best agglomerating temperature at which the metal can best be brought together into a single lump from its distribution in sprouts and smaller particles suspended throughout the electrolyte, is much higher than the most efficient electrolyzing temperature. Furthermore, a violent passage of the electric current tends to aid agglomeration, whether because of electric osmose or electric difference in potential between particles, tending to promote immediate contact and union of the particles, or for other reasons. Finally, we have found that such strong currents tend to produce local overheating unless the electrolyte is strongly agitated from time to time. Therefore, preparatory to shutting down the run, we turn on the heating torch full blast or hard enough to heat the lower portion of the pot nearly to its softening point, and we also increase the current to about 1500 amperes and stir up the charge in the cell thoroughly about every half hour for the two or three last hours of the run. At the end of the twenty-seventh hour, the contents of the cell should be in a nice liquid condition. and the current may be shut off,

the anode taken out and the bath gently but thoroughly stirred for about five minutes, care being taken to cease stirring well be- 1 fore the bath begins to stiffen up at all. If

2000 amperes, but the same general prin-' ciples and methods apply.

Referring to Fig. I of the sheet of drawings, 1 represents the pot of cast-iron high in carbon and .silicon. The pot is surrounded and supported by brickwork 2 and spaced therefrom, an opening being provided in the brickwork at 3 for the insertion of the gas flame torch 4. Fixed over the pot 1 is a hood 5 of cast iron,part of which, at 6, is easily res movable by means of a handle 7 .to permit electrolyte to be inserted. The top of the hood is provided with an insulating plate 8 of suitable heat insulating material such as transite made by the Johns-Manville (10., having a central opening through which passes the anode 9. The hood is provided with an outlet at 10 for collection of the chlorin evolved. The anode is supported by a yoke 11, having a screwthreaded portion passing through a supporting arm" 13, and provided with a hand nut 14 on top of the arm 13, by means of which the position of the anode may be finely adjusted.

When clay pots, like battersea, are used, the cathode 16 should be introduced through a cooled neck or extension 15 in the bottom of the pot, as indicated in Fig. 2, and the space 18 between the cathode and the neck 15 packed with clay or asbestos string, or both, or the packing made of electrolyte cast into place. In case such clay pots and cathodes are used, the relative cathode area to anode area is, of course, different from that specified above and the necessity of auxiliary heat is reduced by reason of the non-conductivity of,the pot, so that with thick pots and large currents it may even be eliminated almost Wholly. When using these clay pots, as above described, the same anode current density is desirable and also the same relative position of the anode,z'. 6., the anode is nearer to the cathode accumulation of metal than to any conducting point on the side of the pot. Also, the same means for supporting and adjusting the anode and a similar hood for the pot may be used.

While we have described our improvements in great detail and with reference to certain specific examples, it is to be understood that we do" not desire to be limited thereto, since many changes and modifications may be made and certain features of novelty may be omitted without departing from the spirit and scope of the invention in its broader aspects. Hence, it is intended to cover all processes coming Within the language of any one or more of the appended claims,

What We claim and desire to secure by Letters Patent is:

l. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the salt to cause deposition of the metal at a terminal Voltage of less than 12 volts with a current density at the anode of less than 8 amperes per square inch While maintaining the temperature of the bath at about 850 C. throughout the greater part of the electrolysis, the electrolyte being sulliciently pure to permit of agglomeration of the metal in the electrolytic bath.

2. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the fused salt to cause deposition of the metal at a terminal voltage of less than 12 volts and with an amperage of substantially over 200 amperes.

3.'The process of producing metallic cerium, and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the fused salt during a substantially continuous run of not less than eight hours to cause deposition of the metal with a current density at the anode of less than 8 amperes per square inch.

l. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the salt to cause deposition of the metal While maintaining the temperature of the bath at about 850 (1. throughout the greater part of the electrolysis.

5. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the fused salt during a substantially continuous run of notices than eight hours to cause deposition of the metal, the electrolyte being sulficiently pure to permit of the electrolysis being continued for substantially eight hours without material clogging of the bath and to permit of agglomeration of the metal in the electrolytic 6. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing chlorid of the metal containing less than 15% of sodium chlorid and electrolyzing the fused chlorid at a terminal voltage of less than 1:2 volts and with an amperage of over 200 amperes.

7. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing chlorid of the metal containing less than 15% of sodium or potassium chlorid and electrolyzing the fused chlorid with a current density at the anode of less than 8 amperes per square inch, the electrolyte being sufficiently pure to permit of agglomeration of the metal in the elec trolytic bath.

8. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing fused chlorid of the metal and electrolyzing the same during a substantially continuous run of not less than eight hours while maintaining the temperature of the bath at about 850 C. throughout the greater part of the electrolysis, the electrolyte being sulliciently pure to permit of agglomeration of the metal in the electrolytic bath.

9. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing fused chlorid of the metal and electrolyzing the same and before the deposited metal is removed from the electrolytic bath treating the bath by in creasing the current to promote agglomeration of the metal therein.

10. The process of producing metallic cerium and similar rare earth metals which consists in preparing a. salt of the metal and electrolyzing the fused salt to cause deposition of the metal and treating the bath occasionally by mechanical agitation during electrolysis to promote agglomeration of the deposited metal.

11. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the fused salt to cause deposition of the metal and treating the bath by increasing the temperature of the bath through external application of heat approximately at the endof the electrolysis to promote agglomeration of the deposited metal therein.

12. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the fused salt to cause deposition of the metal and treating the bath byincreasing the temperature thereof and agitation to produce agglomeration of the decerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the fused salt to cause deposition of the metal and raising the temperature of the bath at the end of the electrolysis to promote agglomeration of the deposited metal therein.

14:. The process of manufacturing metallic I cerium and similar rare earth metals which consists in preparing fused chlorid of the metal and electrolyzing the same while maintaining the temperature of the bath at about850 C. throughout the greater part of the electrolysis and raising the temperature of the bath at the end of the electrolysis to about 950 C. to promote agglomeration of the deposited metal.

15. The process of manufacturing metallic cerium and similar rare earth metals which consists in converting gas mantle waste containing cerium into the form of fused cerium chlorid and electrolyzing the fused cerium chlorid during a substantially continuous run of not less than eight hours to cause deposition of the metal by electrolysis, the cerium chlorid product of the gas mantle Waste being sufficiently pure to permit of the electrolysis being continued for substantially eight hours without material clogging of the electrolytic bath.

16. The process of manufacturing metallic cerium and similar rare earth metals which consists in converting gas mantle waste containing cerium into the form of cerium chlorid, reducing the quantity of impurities which materially prevent agglomeration of the deposited metal when the chlorid is electrolyzed, and electrolyzing the fused cerium chlorid during a substantially continuous run of not less than eight hours to cause deposltion of the metal by electrolysis.

17. The process of manufacturing metallic cerium and similar rare earth metals which consists in converting gas mantle waste con taming cerium into the form of cerium chlorid and electrolyzing the fused cerium chlorid to cause deposition of the metal by electrolysis at a terminal voltage substantially below 12 volts and treating the bath to promote agglomeration of the'deposited metal.

18. The process of manufacturing metall1c cerium and similar. rare earth metals which consists in preparing fused chlorid of the metal and electrolyzing the same and maintaining the temperature of the bath at about 850 during the major portion of the electrolysis by application of heat mainly to the bottom of the electrolyte.

19. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and applied mainly to the bottom of the electrolvte. I 21. The process of producing metalli cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the fused salt to cause deposition of the metal,- the electrolyte introduced into the electrolytic bath containing none or less than 3% of each of the following: sulphur acids or their compounds, phosphorous acids or their compounds and multivalent chlorin carriers.

22. The process of manufacturing metals lic cerium and similar rare earth metals which consists in converting gas mantle waste containing cerium into the form of cerium chlorid, purifying the metal chlorid so that it contains none or less than 3% of each of the following: sulphur acids or their compounds, phosphorous acids or thelr compounds and multivalent chlorin carriers, and electrolyzing the fused cerium chlorid to cause deposition of the metal by electrolfused chlorids to electrolysis to cause deposition of the rare earth metal or metals by electrolysis.

25. The process of manufacturing metallic cerium and similar rare earth metals which consists in dehydrating a composition of the rare earth chlorid in the presence of a gaseous chlorinating agent to produce an electrolyte substantially free from oxychlorid, and electrolyzing the fused metal chlorid to cause deposition of the metal by electrolysis, and recovering the chlorin of the chlorinating agent, in the presence of which the chlorid is dehydrated, and again using the chlorin in the preparation of further electrolyte.

26. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing an electrolyte of rare earth chlorid and alkali metal chlorid substantially free from oxychlorid, and electrolyzing the fused chlorids to cause deposition of the rare earth metal by electrolysis, the electrolyte containing less than 15% of alkali metal chlorid before being fused in the electrolytic cell.

27. The process of producing metallic cerium and similar rare earth metals which consists in preparing an electrolyte comprising a salt of the rare earth metal and a salt of an alkali metal, and electrolyzing the fused salts the electrolyte containing less than 15% of the alkali before being fused in the electrolytic cell.

28. The process of making metallic cerium and similar rare earth metals which consists in fusing chlorid of the metal in a pot of cast iron high in carbon and silicon to purify the chlorid and then electrolyzing the fused chlorid to cause deposition of the metal by electrolysis.

29. The process of making metallic cerium and similar rare earth metals which consists in electrolyzing fused chlorid of the metal in a pot of cast iron high in carbon and silicon.

30. The process of making metallic cerium and similar rare earth metals which consists in fusing an electrolyte of chlorid of the metal and boiling the fused electrolyte for about twenty minutes or more to remove objectionable volatile compounds and subjecting the electrolyte to electrolysis to cause deposition of the metal.

31. The process of making metallic cerium and similar rare earth metals which consists in electrolyzing the fused chlorid of the metal and adding to the electrolytic bath hot solid portions of the chlorid to regulate the temperature of the bath.

32. The process of making metallic cerium and similar rare earth metals which consists in electrolyzing the fused chlorid of the metal and adding to the electrolytic bath hot solid portions of the chlorid to regulate the temperature of the bath, said hot solid portions having been substantially freed from moisture by heating the same in an atmosphere containing a chlorinating agent.

33. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the fused salt to cause deposition of the metal, the electrolytic bath being built up and increased in volume beyond the original volume during the electrolysis by the addition of further electrolyte.

34. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the salt to cause deposition of the metal, the electrolytic bath being gradually built up during the electrolysis by the periodic addition of electrolyte at the rate of about four pounds per thousand amperes per hour.

35. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the fused salt to cause deposition of the metal at a terminal voltage of less than 12 "olts, the electrolytic bath being gradually built up during the electrolysis by the periodic addition of electrolyte.

36. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing an electrolyte salt of the metal and electrolyzing the fused salt at a terminal voltage of substantially less than 12 volts while maintaining the upper electrode within less than one inch from the conducting body of mctallized material electrolyzed.

37. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the fused salt to cause deposition of the metal while maintaining an atmosphere of chlorin substantially free from air about the anode.

38. The process of producing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal and electrolyzing the fused salt to cause deposition of the metal while protecting the anode in the electrolytic bath above the surface of the bath with a coating of the electrolyte.

39. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing chlorid of the metal and electrolyzing the fused chlorid while maintaining an atmosphere of chlorin substantially free from air about the anode and while protecting the anode in the electrolytic bath above the surface of the bath with a coating of the electrolyte.

40. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing chlorid of the metal and electrolyzing the fused chlorid, the current density at the cathode being about one-fourth to one-third as great as it is at the anode.

41. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal containing less than 15% of sodium or potas sium' chlorid and electrolyzing the fused salt at a terminal voltage of substantially less than 12 volts.

42. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal containing less than 15% of sodium or potassium chlorid and electrolyzing the fused salt at a terminal voltage of less than 12 Volts and at a temperature in the neighborhood of 850 C. and suflicient to cause didymium, if present, to'amalgamate with the cerium instead of separating inpulverulent form.

. 43. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal containing less than 15% of sodium or potassium chlorid and electrolyzing the fused salt at a terminal voltage of substantially less than 12 volts and with a cathode current density sufficient to cause lanthanum and didymium, if present, to separate out with the cerium.

44C. The process of manufacturing metallic ture of about 850 C. with a cathode current density suflicient to cause lanthanum and didymium, if present, to separate out with cerium.

45. The process of manufacturing metallic cerium and similar rare earth metals which consists in preparing a salt of the metal containing less than 15% of sodium or potassium chlorid and electrolyzing the fused salt at a temperature in the neighborhood of 850 C. and sufficient to cause didymium, if present, to amalgamate with the cerium instead of separating in pulverulent form.

Signed at New York, in the county of New York and State of New York, this 31st day of August, A. D., 1917.

' ALGAN HIRSCH. MARX HIRSCH. 

